Electric motors are used in a wide variety of applications. In many of these applications, the weight of the motor is of critical importance. For example, in an electric car the overall weight of the vehicle is an important factor limiting the distance that the vehicle can be operated given a fixed battery capacity. However, given current designs, the electric motor itself can be among the heavier components in the vehicle. Thus while it is desirable to provide an electric motor have a high-power output for vehicle use, it is also desirable to have such a motor remain at a lower weight.
It will be appreciated that lighter weight electrical motors are otherwise desirable in many other applications as such motors and the manufactured goods in which such electric motors are incorporated are more easily transported, carried, manipulated, and used. Further, cost reductions and recycling advantages can be obtained where weight reductions are achieved by lighter weight electrical motors that require less material.
However, conventional wound motor designs do not readily lend themselves to weight reduction. One reason for this is that conventional wound coil motor designs require an armature or a stator having coiled conductors thereon. The coils are typically formed by winding wire on metallic laminates. The laminates provide shaped features about which the coils, typically made from a metal such as copper, can be wound.
These laminates add significant mass to the motor. This mass affects the operation of the system in which the motor is used by lowering the power-to-weight ratio of the system. In some cases, eddy currents can arise in the laminates, further reducing motor efficiency and lowering power-to-weight ratios.
In the case of an armature, the laminate mass can cause motor inefficiency in two additional ways. First, this laminate mass increases the inertia that must be overcome to start and stop rotation. Second, the laminate mass is at a distance from the axis of rotation of the armature. In an armature that has a shaft that has any eccentricity, or that has laminates that are not aligned with the shaft, this can create static and dynamic balance problems that consume energy. Additionally, shaft eccentricity and misaligned laminates affect the placement of the windings on the laminates, so the effects of any shaft eccentricity or laminate misalignment are further enhanced by the mass of the windings.
One effort to reduce the use of such laminates involves pancake or flat motors. Conventional flat motors are used in a variety of applications. For example, U.S. Pat. No. 8,076,808 describes a flat vibration motor, such as can be used in a cellular telephone. EP 0548362A1 describes construction of a typical prior-art flat motor, also known as a “pancake motor.” The example described is a flat coreless DC motor having flat armature coils mounted on a disk. The coils are wound into sectors of the disk. The disk can be the rotor and can be mounted over a stator including a field magnet. When current is passed through the coils via a commutator, the rotor turns.
Various ways of manufacturing pancake motors, and specifically windings and rotors for pancake motors, have been described. WO 2009/038648 describes applying insulating material over a pre-formed electrical conductor and heating the assembly to activate an adhesive that bonds the insulating material to the conductor. However, this requires an insulator that includes the heat-activated adhesive, and requires that the conductors be formed to shape before being insulated.
U.S. Patent Publication No. 2002/0105237 describes a stator for a planar linear motor. The stator includes magnetic sheets (i.e., sheets of a material that can complete a magnetic circuit) set vertically and bound together, e.g., using a fluid hardening material or an epoxy resin.
However, such pancake motors use laminate structures that extend typically further from an axis of rotation than do conventional motors, creating increased balance problems, and adding weight. Further such motors have limited performance characteristics compared to conventional wound laminate motors.
What is needed in the art are motors that provide conventional performance characteristics while offering reduced motor mass. What is also needed in the art are new methods for motor manufacture.